In the Introduction to the second edition of his The Rise of Western Christendom (also see the BMCR review of the first edition here) renowned scholar of late antiquity Peter Brown writes:
In fact, the world in which Muhammad lived was one in which whole communities of Arabs had already converted to either Christianity or Judaism. Yemen, for example, at the southernmost reaches of the Arabian peninsula, was already "conquered" by Christianity, as Brown puts it, before Muhammad was born, but this did not take place until afterIslam did not come out of nowhere. Nor did it instantly blot out all that had come before it ... Islam emerged in an Arabian environment thoroughly penetrated by Christian and Jewish ideas.[p. 3]
Brown even points out that such a free and open exchange of different religious ideas "would have been unthinkable in the orthodox empire of Justinian"!! This free and open discussion of religious ideas was not limited to Yemen in the south and the frontiers of Rome and Persia to the north, but was ongoing throughout the Arabian peninsula:the pros and cons of Christianity and Judaism had been hotly debated, in Arabic and in a manner which resounded throughout the Arab world.[p. 288]
Some tribes of central Arabia had adopted Judaism. Others, such as the Banu Ghassan, were known for their Christianity. Religious differences were part of the ceaseless battle for prestige between the tribes. Faced by an open world, already polarized between Jews and Christians, Persians and East Romans, the dominant family of Mecca, the Quryash, were proud to remain frank idolaters. In a world where Jews and Christians, and even the great empires of the Near East, had come uncomfortably close, they thought it best to stand to one side and wait.[pp. 290-291]
Not so Muhammad. In 610, at the age of 40, the visions began to come. They came from the One God (in Arabic: Allah), "the Lord of the Worlds". For the next 20 years the messages came irregularly, in sudden shattering moments, up to his death in 632. In them, so Muhammad believed, the same God who had spoken to Moses and to Jesus, and to many thousands of humbler prophets, now spoke again, once and for all, to himself. Vivid sequences of these words from God were carefully memorized by Muhammad's followers. They were passed on by skilled reciters throughout the Arabic-speaking world. For these were nothing less than snatches of the voice of God himself speaking to the Arabs through Muhammad....
What Muhammad recited was ... a direct rendering of the eloquence of God as he spoke to the human race. This God had never ceased , throughout the ages, to "call out" to all nations, through his many prophets. Now this voice repeated itself, in Arabic, in a final and majestically definitive summation.
it was this aspect of the Quran which instantly offended Jews and Christians. For the messages relayed by God through Muhammad claimed to undo the past. His messages declared that neglect and partisan strife had caused Jews and Christians to slip away from, even to distort, the messages which they had once received from their prophets, Moses and Jesus....
The name adopted by the new religion, "Islam", and the word used to describe its adherents, "Muslims", came from the same Arabic root, slm -- to surrender, to trust in one God. It summed up an entire view of history. It was a history where, in what truly mattered for human beings -- that is, their relationship with God -- nothing had ever changed. Islam and Muslims had always existed. In all past ages, trust in God and the rejection of all other worship had invariably distinguished true monotheists from ignorant polytheists. God had fostered this monotheism by sending his prophets to the Jews and to the Christians....